Why is the cell membrane impermeable to some ions and glucose, but is permeable to alcohol and urea?

Hydrogen bonds are present in both urea and alcohols with nitrogen and oxygen, respectively.

This implies that, like other polar molecules (like water) and non-polar molecules, they can display both polar and non-polar properties and can therefore pass through the bi-layer.

But, because they are physically too large to pass through the bi-layer, ions and glucose, on the other hand, require channel proteins.

While alcohol and urea are small, nonpolar molecules that can pass through the lipid bilayer via simple diffusion, some ions and glucose are polar molecules and ions that cannot easily pass through the hydrophobic interior of the lipid bilayer, making the cell membrane impermeable to them.

The cell membrane is selectively permeable due to its structure and composition. It allows certain substances to pass through while blocking others. Small nonpolar molecules like alcohol and urea can diffuse through the lipid bilayer of the membrane due to their ability to dissolve in lipids. However, ions and larger polar molecules like glucose cannot easily pass through the lipid bilayer because of their charge and size. Instead, they typically require specific transport proteins or channels to facilitate their passage across the membrane. This selective permeability ensures the proper functioning of the cell and helps maintain internal conditions suitable for cellular processes.